I started going over the large-print edition on the computer--I think it works, because at least I can immediately hop back into the Scribus file and fix whatever looks off. I've done seven chapters so far.
I'm a little nervous because I'm making aesthetic decisions, like I changed the chapter number because I thought it wasn't dramatic enough. I think I'll print out a full-sized copy of a couple of spreads just to ensure that I'm making the right call there.